A typical prior art switch is shown and disclosed in U.S. Pat. No. 3,164,701 assigned to the assignee of the instant invention. In that patent a switch is shown which comprises a housing in which a switch cavity is formed. A stationary contact and a flexible, cantilever mounted movable contact arm are mounted in the switch cavity. An opening is formed in the housing which is closed by a thermally conductive cap trapping a snap-acting, thermally responsive disc between the cap and the housing. A motion transfer pin is slidably disposed in the housing extending between the movable contact arm and the disc so that when the disc snaps from one configuration to another, its motion is transferred to the movable contact arm to open or close the electrical connection between the stationary contact and the movable contact arm.
Switches of this type have been very effective and many hundreds of thousands have been made and sold throughout the world, however, such switches have certain limitations in today's market place. For example, calibration of the switch is required including positioning of the stationary terminal by bending the support on which the stationary contact is mounted and bending of a separate member overlying the movable contact arm in order to obtain a desired contact force. Such calibration not only requires extra parts such as calibration screws, but also adds significantly to the cost of assembly. Further, such switches are designed to carry appreciable current, in the order of 10 to 15 amps, for example, thus serving to limit the design of the movable arm. In order to conduct the required current as well as to provide suitable contact force of typically one or two ounces in the small available space, a relatively high spring rate has been required for the movable contact arm, for example, in excess of ten pounds per inch.
It is an object of the present invention to provide a thermally responsive electrical switch which is easily produced and assembled, one which requires no calibration or gauging yet has conventional contact force. It is another object of the invention to provide such a switch which has fewer parts than conventional switches and which can be more economically manufactured. Other objects, features and methods will be in part pointed out hereinafter.